During the surgical removal of a tumor, the problem arises that healthy tissue frequently cannot be distinguished with the naked eye from a tissue affected by a tumor. In order to provide a remedy here, the patient is administered before the operation with a fluorescent dye that is specifically enriched in the tumor. During the operation, the exposed tissue is illuminated with a light in the near infrared region that is suitable for exciting the fluorescent dye. The tissue is recorded with the aid of an image acquisition device that has an optical unit for separating a fluorescent image generated by the fluorescent light, and a native tissue image formed by the ambient light. The recorded fluorescent images and the tissue images are superimposed by way of an image processing device, the tumorous tissue being labeled in the superimposed image by way of, for example, a false color display.
The fluorescent light emitted by the fluorescent dye has a substantially lower intensity by comparison with the ambient light. The fluorescent image must be highly intensified for the purpose of generating images. The problem arises here that the ambient light also includes spectral fractions that correspond to the fluorescent light emitted by the fluorescent dye. These interfering spectral fractions are also intensified during the generation of images and falsify the fluorescent images.
In order to counteract this disadvantage, an attempt is made according to the known systems, to raise the intensity of the fluorescent light emitted by the fluorescent dye. Use is made to this end of a strong exciting light source that includes LEDs for generating light in the near infrared region. The LEDs are operated in a pulsed or clocked fashion in order to attain a particularly high power. It is true that success is thereby achieved in reducing the influence of the interference signal in the generation of images. However, the generation of as exact a fluorescent image as possible entails the aim of further reducing the interference signal or completely suppressing it.